In the semiconductor device such as LSI or the like, a large number of contact holes are formed in the insulating film to get the electrical connection between layers. The conductive plugs are buried in the contact holes, and then the source/drain regions of the MOS transistors formed in the surface layer of the semiconductor substrate are connected to overlying metal wirings via the conductive plugs.
Meanwhile, when the contact hole is not opened, the conductive plug does not get to the source/drain region, and thus the source/drain region and the metal wiring are not connected electrically mutually. Such defect is called the contact failure, and acts as a cause of lowering yield of the semiconductor device.
The related arts of the present embodiments are disclosed in Japanese Laid-open Patent Publication No. 2002-43237 and Japanese Patent No. 3556437.